1. Field of the Invention
The present invention relates to a substrate cooling apparatus, a substrate cooling method, and a storage medium.
2. Description of the Related Art
In a coating and developing apparatus for forming a resist pattern, a wafer cooling apparatus called a cooling plate for cooling a semiconductor wafer (hereafter, referred to as a wafer) which has been subjected to heat-processing is provided. This wafer cooling apparatus cools (temperature-regulates) the wafer before a coating film such as a resist is formed, to set the wafer to a predetermined temperature. The coating film forming processing is performed after the cooling, whereby the film can be formed with high uniformity for each wafer. Further, the wafer is cooled by the wafer cooling apparatus also before the developing treatment, whereby the uniformity of the line width of the pattern can be improved.
The wafer cooling apparatus includes a mounting table for mounting the wafer thereon, and the mounting table surface is temperature-controlled by a so-called chiller. Describing in more detail, circulation paths through which cooling water temperature-controlled by a common chiller flows are provided in mounting tables, and the cooling water cools the mounting table surfaces. This can cool the wafer mounted on the mounting table.
Incidentally, to improve the throughput of the coating and developing apparatus, the improvement in the cooling speed of the wafer cooling apparatus is being studied. However, to cool the wafer mounted on each of the mounting tables to a cooling target cooling target temperature, for example, 23° C., the cooling water needs to be controlled at a temperature corresponding to the target temperature. In other words, the cooling temperature of the cooling water is limited by the cooling target temperature. Accordingly, in the case where a plurality of wafer cooling apparatuses are provided in the coating and developing apparatus, even if the temperatures of the wafers mounted on the mounting tables are different from each other, the cooling water at the same temperature has to be supplied to them, so that it may be difficult to rapidly cool the wafers in some cases. Further, it is also conceivable to provide a plurality of chillers to be able to control the temperature of the cooling water independently for each of the wafer cooling apparatuses, and individually control the temperature of the cooling water to thereby improve the throughput, which leads to increased cost.
For the above reason, cooling of the wafer by supplying a cooling gas to a space between the mounting table and the rear surface of the wafer mounted there on as well as performing the cooling by the cooling water is discussed, and a substrate cooling apparatus thus configured is disclosed in, for example, Japanese Patent Application Laid-open No. H11-195599 (paragraph 0093, FIG. 19 and FIG. 22). However, a problem when cooling is performed using the cooling gas is that it is difficult to cool the wafer with high uniformity by controlling the flow of the gas. If a resist or a chemical for forming various kinds of films is supplied in the state where the temperature is nonuniform within the wafer because of insufficient control of the cooling gas, the film thickness may become nonuniform within the wafer. Further, when a developing solution is supplied in this state, the line width of the resist pattern may differ within the wafer.
For example, in Japanese Patent Application Laid-open No. H11-195599, the unevenness of the gas flow on the lower surface of the substrate can be prevented by forming a projection on the mounting table in a line shape along the circumferential direction of the substrate. However, when such a projection is provided, the projection actually blocks the gas flow to make it difficult for the cooling gas to spread to the inside of the projection, so that the cooling with high uniformity may be difficult. Further, in Japanese Patent Application Laid-open No. H07-153749 (paragraph 0033 and FIG. 5), the method of supplying a cooling gas at a temperature lower than the target temperature to the substrate and then bringing the cooling gas to the target temperature to thereby rapidly cool the substrate is described, but the means for cooling the substrate with high uniformity is not described.